System and method for transmitting real-time-critical and non-real-time-critical data in a distributed industrial automation system

ABSTRACT

A system and a method provide a real-time-critical communication and a non-real-time-critical communication in a switched data network consisting of users and switching units, for example a distributed automation system, by a cyclic operation. In a transmission cycle, there exists for all users and switching units of the switched data network in each case at least one section for transmitting real-time-critical data and at least one section for transmitting non-real-time-critical data, as a result of which the real-time-critical communication is separated from the non-real-time-critical communication. Since all users and switching units are always synchronized to a common time base, the respective sections for transmitting data in each case take place at the same time for all users and switching units, i.e. the real-time-critical communication takes place independently in time from the non-real-time-critical communication.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/243,906 filed Oct. 1, 2008 now U.S. Pat. No. 8,064,482. The U.S.application with Ser. No. 12/243,906 is a continuation application ofU.S. application Ser. No. 09/790,998 filed Feb. 22, 2001. Thisapplication claims priority of German patent application No. 10058524.8DE filed Nov. 24, 2000. All of the applications are incorporated byreference herein in their entirety.

FIELD OF INVENTION

The invention relates to a system and a method for the paralleltransmission of real-time-critical and non-real-time-critical data viaswitched data networks, especially the Ethernet.

BACKGROUND OF INVENTION

Data networks provide for the communication between a number of usersdue to the networking, that is to say the connection of the individualusers to one another. Communication here means the transmission of databetween the users. The data to be transmitted are sent out as datatelegrams, i.e. the data are packed together to form a number of packetsand are sent via the data network to the corresponding receiver in thisform. They are, therefore, also called data packets. The termtransmission of data is used completely synonymously to theabove-mentioned transmission of data telegrams or data packets in thisdocument. The question of networking itself is solved, for example inthe case of switched high-performance data networks, especially theEthernet, by in each case at least one switching unit being connectedbetween two users which is connected to both users. Each switching unitcan be connected to more than two users. Each user is connected to atleast one switching unit but not directly to another user. Users are,for example, computers, stored program systems (SPS) or other machineswhich exchange, especially process, electronic data with other machines.In contrast to bus systems in which each user can reach any other userof the data network directly via the databus, the switched data networksare exclusively point-to-point connections, i.e. a user can only reachall other users of the switched data network indirectly by correspondingforwarding of the data to be transmitted by means of one or moreswitching units.

In distributed automation systems, for example in the field of driveengineering, certain data must arrive at certain times at the usersintended for them and must be processed by the receivers. These arecalled real-time-critical data or data traffic since any untimelyarrival of the data at the destination leads to unwanted results at theuser. According to IEC 61491, EN61491 SERCOS interface-brief technicaldescription, a successful real-time-critical data traffic of theabovementioned type can be guaranteed in distributed automation systems.

SUMMARY OF INVENTION

It is an object of the invention to specify a system and a method fortransmitting data via switched data networks, especially the Ethernet,which provides for mixed operation of real-time-critical andnon-real-time-critical data communication, especially Internet- orIntranet-based data communication, in the same data network.

The teachings hereinbelow extend to those embodiments which fall withinthe scope of the appended claims, regardless of whether they accomplishone or more of the above-mentioned needs.

This object is achieved by a method for transmitting data via switcheddata networks, especially the Ethernet, in the field of industrialsystems, in which real-time-critical and non-real-time-critical data aretransmitted, the switched data network being set up between at least twousers, especially a transmitter and a receiver, the data beingtransmitted in at least one transmission cycle with adjustable period,each transmission cycle being subdivided into at least one first sectionfor the transmission of real-time-critical data for real-time controland at least one second section for the transmission ofnon-real-time-critical data.

This object is achieved by a system for transmitting data via switcheddata networks, especially the Ethernet, in the field of industrialsystems, comprising at least one data processing device which can becoupled to a data network and which transmits real-time-critical andnon-real-time-critical data, the switched data network being set upbetween at least two users, especially a transmitter and a receiver, thesystem exhibiting means for transmitting data in at least onetransmission cycle with adjustable period, each transmission cycle beingsubdivided into at least one first section for transmittingreal-time-critical data for real-time control and at least one secondsection for transmitting non-real-time-critical data.

The invention is based on the finding that an open, Internet-basedcommunication is spontaneous communication, i.e. that both the time ofsuch type of communication and the volume of data arriving which must betransferred during communication cannot be determined in advance. As aresult, collisions on the transmission lines in the case of bus systemsor in the switching units in the case of switched high-speed networks,especially Fast Ethernet or Switched Ethernet, are not impossible. To beable to utilize the advantages of the Internet communication technologyalso in real-time communication in switched data networks in the fieldof automation engineering, especially drive engineering, mixed operationof real-time communication with other spontaneous non-real-time-criticalcommunication, especially Internet communication, is desirable. This ismade possible by the fact that the real-time communication which occurspredominantly cyclically in the fields of application considered hereand can thus be planned in advance is strictly separated from thenon-real-time-critical communication, especially the open,Internet-based communication, which, in contrast, cannot be planned.

Communication between the users is effected in transmission cycles, eachtransmission cycle being subdivided into at least one first section fortransmitting real-time-critical data for real-time control, for exampleof the industrial systems provided therefor, and at least one secondsection for transmitting non-real-time-critical data, especially inopen, Internet-capable communication. An especially advantageousembodiment of the invention is characterized by the fact that each useris allocated a switching unit which is provided for transmitting and/orreceiving and/or forwarding the data to be transmitted.

An extremely advantageous embodiment of the invention is characterizedby the fact that all users and switching units of the switched datanetwork always exhibit a common synchronous time base due to mutualtiming synchronization. This is the prerequisite for separating theplannable real-time communication from the non-real-time-criticalcommunication which cannot be planned. Separation of the plannablereal-time communication and the unplannable non-real-time-criticalcommunication is guaranteed by applying the method for timesynchronization in accordance with application DE 10004425.5 which hasnot been previously published. By permanently applying this method alsoduring active operation of a distributed automation system, all usersand switching units of the switched data network are always synchronizedto a common time base which, in consequence, means the same startingpoint and the same length of each transmission cycle for all users andswitching units. Since all real-time-critical data transmissions areknown before the actual data transmission due to the cyclic operation,and, therefore, can be planned in advance, it is ensured that thereal-time communication can be controlled for all users and switchingunits in such a manner that no disturbances, for example collisions,occur in the data transmission of the real-time-critical data telegramsthemselves and all planed critical data transfer times are maintainedprecisely.

Another especially advantageous embodiment of the invention ischaracterized by the fact that all non-real-time-critical data which areintended to be transmitted during the section of a transmission cyclewhich is provided for the real-time critical communication aretemporarily stored by the respective switching unit and are transmittedduring the section of this or a subsequent transmission cycle which isintended for the non-real-time-critical communication, i.e. anyunplanned Internet communication which may occur in the first section ofa transmission cycle which is reserved for the real-time communicationis shifted into the second section of the transmission cycle which isreserved for the spontaneous non-real-time-critical communication as aresult of which disturbances of the real-time communication arecompletely prevented. The corresponding data of the spontaneousnon-real-time-critical communication are temporarily stored by theswitching unit affected in each case and are only transmitted in thesecond section of the transmission cycle which is reserved for thespontaneous, non-real-time-critical communication after the section forthe real-time communication has expired. This second section, i.e. thetotal period up to the end of the transmission cycle, is available toall users for the non-real-time-critical communication, especiallyInternet communication, which cannot be planned, also withoutinfluencing the real-time communication since this is performedseparately in time.

Collisions with the real-time-critical data telegrams in the switchingunits can be prevented by all non-real-time-critical data which cannotbe transmitted during the section of a transmission cycle intended forthe transmission of the non-real-time-critical data being temporarilystored by the respective switching unit and transmitted during thesection of a later transmission cycle which is intended for thetransmission of the non-real-time-critical data.

A further advantageous embodiment of the invention is characterized bythe fact that the period of the section for the transmission ofnon-real-time-critical data within a transmission cycle is automaticallyestablished by the period of the section for the transmission ofreal-time-critical data. The advantage of this arrangement is that ineach case it is only the necessary transmission time for thereal-time-critical data traffic which is used and the remaining time isautomatically available for the non-real-time-critical communication,for example for the Internet communication which cannot be planned or,respectively, other non-real-time-critical applications. It isespecially advantageous that the period of the section for thetransmission of real-time-critical data within a transmission cycle isin each case determined by the data to be transmitted in aconnection-oriented manner, i.e. the period of the two sections isdetermined for each individual data connection by the volume of data ofthe real-time-critical data to be transmitted, which is necessary ineach case, as a result of which the division of the two sections andthus the time available for the non-real-time-critical communication isoptimized for each transmission cycle for each individual dataconnection between two switching units.

A further advantageous embodiment of the invention is characterized bythe fact that the period of a transmission cycle is established at leastonce before the respective data transmission takes place. This has theadvantage that, as a result, the period of a transmission cycle can bematched to the respective requirements for real-time communication or,respectively, for the open Internet-capable communication with eachstart of a new data transmission planned in advance. Naturally, it isalso possible that the period of a transmission cycle and/or the periodof the section for the transmission of real-time-critical data of atransmission cycle can be changed depending on requirement, for exampleat preplanned fixed times and/or after a planned number of transmissioncycles, advantageously before the beginning of a transmission cycle, byswitching to other planned real-time-critical transmission cycles. Theperiod of a transmission cycle is advantageously between one microsecondand ten seconds depending on the application.

Another extremely advantageous embodiment of the invention ischaracterized by the fact that the real-time communication can be newlyplanned at any time during active operation of an automation systemwhich guarantees a flexible adaptation of the real-time control toboundary conditions changing at short notice. This also makes itpossible to change the period of transmission cycle.

A further advantageous embodiment of the invention is characterized bythe fact that a part of the section of the transmission cycle intendedfor the transmission of real-time-critical data is intended for thetransmission of data for the organization of the data transmission. Ithas been found to be of special advantage in this connection that thedata telegrams for the organization of the data transmission aretransmitted at the beginning of the section for the transmission ofreal-time-critical data of the transmission cycle. Data for theorganization of the data transmission are, for example, data for thetiming synchronization of the users and switching units of the datanetwork, data for recognizing the topology of the network, etc.

A further advantageous embodiment of the invention is characterized bythe fact that, for all real-time-critical data telegrams to betransmitted, the transmitting and receiving time at the transmitterand/or receiver, and in all switching units involved in each case alltimes for forwarding the real-time-critical data telegrams and therespective associated links via which the real-time-critical datatelegrams are forwarded are noted before the beginning of the respectiveperformance of the data transmission, i.e. it is noted in a switchingunit when and to which output port a real-time-critical data telegramarriving at time X is to be forwarded.

A further extremely advantageous embodiment of the invention ischaracterized by the fact that the forwarding times are planned in sucha manner that each real-time-critical data telegram arrives at thecorresponding switching unit at the latest at the forwarding time orearlier but is in any case only forwarded at the forwarding time. Thiseliminates the problem of timing uncertainties which becomes noticeableespecially in the case of long transmission chains. As a result, thereal-time-critical data telegrams can be transmitted or forwardedimmediately, without time interval, i.e. poor utilization of thebandwidth in the case of real-time data packets is prevented. Naturally,it is also possible to insert transmission gaps between the transmissionof the individual data packets if necessary.

A further advantage of the time-based forwarding is that finding thedestination is no longer address-based in the switching unit since it isclear from the start which port is the forwarding destination. Thisprovides for optimum utilization of all existing links within theswitched data network. Redundant links of the switched data networkwhich must not be used for the address-based switching through of thenon-real-time-critical communication because otherwise there would becircularities of data packets, however, can be taken into considerationin advance for the planning of the forwarding links and can thus be usedfor the real-time communication. This makes it possible to implementredundant network topologies, e.g. rings for error-tolerant real-timesystems. Data packets can be transmitted redundantly on disjoint pathsand there are no circularities of data packets. A further advantage ofthe preplanned forwarding is that, in consequence, the monitoring ofeach link section is possible without acknowledgement and errordiagnostics can thus be performed in a simple manner.

Another extremely advantageous embodiment of the invention ischaracterized by the fact that at least one arbitrary user, especially auser having the capability for open Internet-capable communication, withor without associated switching unit, can be added to a switched datanetwork and it is then ensured that critical data transfers aresuccessfully performed at the desired time even if the arbitrary userperforms a non-real-time-critical communication, especially an Internetcommunication in parallel with a real-time-critical communication.

Another especially advantageous embodiment of the invention ischaracterized by the fact that a switching unit is integrated in a user.This results in an extraordinary cost advantage compared with theswitching units, also called switches, previously always implemented asindependent modules.

A further advantageous embodiment of the invention is characterized bythe fact that a switching unit exhibits two separate accesses to therespective user, one access being provided for the exchange ofreal-time-critical data and the other access being provided for theexchange of non-real-time-critical data. This has the advantage thatreal-time-critical and non-real-time-critical data are processedseparately. The access for the non-real-time-critical data correspondsto the commercially available interface of a regular Ethernetcontroller, as a result of which the preexisting software, especiallythe drivers, can be used without restriction. The same applies to thepreexisting software for a non-real-time-capable data network.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingdrawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 shows a diagrammatic representation of an exemplary embodiment ofa distributed automation system,

FIG. 2 shows the basic structure of a transmission cycle,

FIG. 3 shows the basic operation in a switched network, and

FIG. 4 shows a diagrammatic representation of the interfaces between alocal user and a switching unit.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a diagrammatic representation of an exemplary embodiment ofa distributed automation system, the switching unit in each case alreadybeing integrated in the respective user as part of the invention forreasons of clear representation. In contrast, the prior art sees each ofthe switching units, here already integrated in the relevant local user,as a separate device which is in each case connected between two users.Integrating the respective switching unit in a user is more inexpensiveand easier to maintain.

The automation system shown consists of a number of users which can beconstructed both as transmitter and as receiver at the same time, forexample of a control computer 1, a number of drives in which only drive2 is designated for reasons of clear representation, and other computers3, 4, 5 which are connected to one another to faun a switched datanetwork, especially the Ethernet, by means of connecting cables,especially Ethernet cables, in the case of which only connections 6 a, 7a, 8 a, 9 a are designated for reasons of clear representation. Theswitching units which are typical of the topology of an Ethernet and inthe case of which only switching units 6, 7, 8, 9, 10 are designated forreasons of clear representation, are already integrated in therespective users in this representation The switching units are used fortransmitting and/or receiving and/or forwarding the data to betransmitted.

Control computer 1 is connected, for example, additionally to anin-house communication network, for example the Intranet 11 and/or theworldwide communication network Internet 11. The control computer 1transmits real-time-critical data, for example for controlling drive 2via connections 6 a, 7 a, 8 a, 9 a. These real-time-critical data mustbe processed by drive 2 precisely at time X since otherwise unwantedeffects occur, such as, e.g. a delayed start of drive 2, which disturbthe operation of the automation system. The real-time-critical data arein each case forwarded by switching units 6, 7, 8, 9 up to switchingunit 10 which transfers them to the receiver drive 2 which processes thedata at time X. In the prior art, a successful real-time-critical datatraffic of the abovementioned type can be guaranteed if, in addition, noother arbitrary communication, for example Internet communication, isperformed by computer 5 at the same time. In this case, Internetcommunication at the same time by computer 5, computer 5 requests, forexample, an Internet page. These non-real-time-critical data areforwarded via connections 8 a, 7 a, 6 a by means of switching units 9, 8and 7 to switching unit 6 which transfers the data to computer 1 which,finally, delivers the corresponding request to the Internet 11 and sendsback the response in the reverse order to computer 5 via the sameconnections and switching units. The response thus uses the same path asthe real-time-critical communication. As a result, a waiting situationmay occur in the switching units involved and the real-time-criticaldata may no longer arrive on time at drive 2. It is, therefore, nolonger possible to guarantee error-free real-time operation with theprior art. Application of the disclosed invention, in contrast, providesfor any non-real-time-critical communication in parallel with thereal-time communication in the same data network without disturbing thereal-time communication. This is indicated by the connection ofcomputers 3 and 4 in which no switching unit is integrated and which areintegrated into the automation system shown by means of a directEthernet connection. Computers 3 and 4 do not participate in thereal-time communication but only in the spontaneous, Internet-capablenon-real-time-critical communication without disturbing the real-timecommunication.

The invention is based on the concept that real-time-critical andnon-real-time-critical communication in switched data networks areseparated from one another in such a manner that thenon-real-time-critical communication does not exert any disturbinginfluence on the real-time-critical communication. The prerequisite forthis separation is, on the one hand, that all users and switching unitsof the switched data network always have a common synchronous time basedue to mutual timing synchronization. This is also guaranteed in theactive operation of a distributed automation system by permanentapplication of the method for timing synchronization according toapplication DE 10004425.5, not previously published. The secondprerequisite for the separation is that the real-time-criticalcommunication can be planned which is given by the fact that thereal-time communication occurs cyclically in the fields of applicationconsidered here, especially drive engineering, i.e. a data transmissiontakes place in one or more transmission cycles.

FIG. 2 shows by way of example the instance of a basic structure of atransmission cycle which is divided into two sections. A transmissioncycle 12 is divided into a first section 13 which is intended for thetransmission of real-time-critical data and a second section 14 which isintended for the transmission of non-real-time-critical data. The lengthof the transmission cycle 12 shown symbolizes its duration 17 in timewhich advantageously is between one microsecond and ten secondsdepending on the application. The period 17 of a transmission cycle 12is changeable but is established at least once before the time of datatransmission, for example by the control computer 1, and has the samelength in each case for all users and switching units of the switcheddata network. The period 17 of a transmission cycle 12 and/or the periodof the first section 13 which is intended for the transmission ofreal-time-critical data can be changed at any time, for example atpreplanned fixed times and/or after a planned number of transmissioncycles, advantageously before the beginning of a transmission cycle 12,by the control computer 1 switching, for example, to other plannedreal-time-critical transmission cycles. In addition, the controlcomputer 1 can newly plan the real-time communication at any time duringthe active operation of an automation system, depending on requirement,as a result of which the period 17 of a transmission cycle 12 can alsobe changed. The absolute period 17 of a transmission cycle 12 is ameasure of the proportion of time or, respectively, the bandwidth of thenon-real-time-critical communication during a transmission cycle 12,that is to say the time which is available for thenon-real-time-critical communication. Thus, the non-real-time-criticalcommunication has, for example, a bandwidth of 30% with a period 17 of atransmission cycle 12 of 500 μs and a bandwidth of 97% with 10 ms. Inthe first section 13 which is intended for the transmission ofreal-time-critical data, a certain period is reserved for transmittingdata telegrams for the organization of the data transmission 15 beforethe transmission of the actual real-time-critical data telegrams ofwhich only the data telegram 16 is designated for reasons of clarity.The data telegrams for the organization of the data transmission 15contain, for example, data for the timing synchronization of the usersand switching units of the data network and/or data for recognizing thetopology of the network. After these data telegrams have been sent, thereal-time-critical data telegrams or, respectively, the data telegram 16are transmitted. Since, due to the cyclic operation, the real-timecommunication can be planned in advance, the transmitting times or,respectively, the times for forwarding the real-time-critical datatelegrams are known for all real-time-critical data telegrams of atransmission cycle 12, or, respectively, the data telegram 16 to betransmitted, before the beginning of the data transmission, i.e. theperiod of the section 14 for the transmission of non-real-time-criticaldata is automatically established by the period of the section 13 fortransmitting real-time-critical data. The advantage of this arrangementis that in each case only the transmission time needed for thereal-time-critical data traffic is used and after this has ended, theremaining time is automatically available for the non-real-time-criticalcommunication, for example for the Internet communication, which cannotbe planned, or other non-real-time-critical applications. It isespecially advantageous that the period of the section 13 fortransmitting real-time-critical data is in each case determined by thedata to be transmitted in a connection-oriented manner, i.e. the periodof the two sections is determined by the volume of data of thereal-time-critical data to be transmitted which is in each casenecessary for each individual data connection, as a result of which thedivision of section 13 and section 14 in time can differ for eachindividual data connection for each transmission cycle 12. In each caseonly the necessary transmission time for the real-time-critical datatraffic is used and the remaining time of a transmission cycle 12 isautomatically available for the non-real-time-critical communication,for example for an Internet communication which cannot be planned or,respectively, other non-real-time-critical applications for all users ofthe switched data network. Since the real-time communication iscorrespondingly planned in advance in such a manner that the arrival ofthe real-time-critical data telegrams in the corresponding switchingunits is planned in such a manner that the real-time-critical datatelegrams considered, for example data telegram 16, arrive at thecorresponding switching units at the forwarding time at the latest orearlier, the real-time-critical data telegrams or, respectively, datatelegram 16 can be transmitted or forwarded without time interval sothat the available period is used in the best possible way due to thedensely packed transmission or forwarding. Naturally, it is alsopossible to insert transmission gaps between the transmission of theindividual data telegrams if necessary.

FIG. 3 shows the basic operation in a switched network. Representativeof a network, a user 18, for example a drive, and a user 19, for examplea control computer, are shown, having in each case integrated switchingunits 20, 21 and a further user 36 without switching unit which areconnected to one another by the data connections 32, 33. In thisarrangement, the switching unit 20 is connected to the switching unit 21via the external port 30, the data connection 32 and the external port31. The other external ports shown on the switching units 20, 21 havenot been designated for reasons of clarity of the illustration. Otherusers with or without integrated switching unit have also not been shownfor reasons of clarity of the illustration. Data connections 34, 35 toother users and coming from the switching units 20, 21 shown are onlyindicated. Switching units 20, 21 in each case have local memories 24,25 which are connected to users 18, 19 via the internal interfaces 22,23. The users 18, 19 exchange data with the corresponding switchingunits 20, 21 via the interfaces 22, 23. The local memories 24, 25 areconnected to the processors 26, 27 within the switching units 20, 21 viathe data connections 28, 29. The processors 26, 27 receive data or,respectively, forward data via the internal data connections 28, 29 fromand, respectively, to the local memories 24, 25 or via one or more ofthe external ports, for example port 30 or port 31. The switching units20, 21 always have a common synchronous time base due to the applicationof the method of timing synchronization. If user 19 hasreal-time-critical data, these are fetched by the processor 27 via theinterface 23, the local memory 25 and the connection 29 during thesection for the real-time-critical communication at the preplanned timeand are transmitted from there to the switching unit 20 via the intendedexternal port, for example port 31. If user 36 transmitsnon-real-time-critical data, for example for an Internet request, at thesame time, that is to say during the real-time-critical communication,via the data connection 33, these data are received by the processor 27via the external port 37 and forwarded via the internal connection 29 tothe local memory 25 where they are temporarily stored. From there, theyare only retrieved in the section for the non-real-time-criticalcommunication and forwarded to the receiver, i.e. they are shifted intothe second section of the transmission cycle which is reserved for thespontaneous non-real-time critical communication which eliminatesdisturbances in the real-time-communication. In the case where not allnon-real-time-critical data temporarily stored can be transmitted duringthe section of a transmission cycle intended for the transmission of thenon-real-time-critical data, they are temporarily stored in the localmemory 25 of the switching unit 21 until they can be transmitted duringa section of a later transmission cycle which is intended for thetransmission of the non-real-time-critical data, which eliminatesdisturbances of the real-time communication in every case.

The real-time-critical data telegrams which arrive at the processor 26of the switching unit 20 via data connection 32 via the external port 30are immediately forwarded via the corresponding external ports. This ispossible since the real-time communication is planned in advance and,therefore, the transmitting and receiving time for allreal-time-critical data telegrams to be transmitted, all switching unitsinvolved in each case and all times for the forwarding and all receiversof the real-time-critical data telegrams are known, i.e. it is noted,for example, in processor 26 of the switching unit 20 that thereal-time-critical data telegrams arriving at time X are to be forwardedto the next switching unit via external port 38. Due to the advanceplanning of the real-time communication, it is also ensured that therewill be no data collisions, for example on data connection 34 from port38. Naturally, the same applies to all other data connections or,respectively, ports during the real-time communication. The forwardingtimes of all real-time-critical data packets from the switching unitsinvolved in each case are also preplanned and thus unambiguouslyestablished. The arrival of the real-time-critical data telegrams, forexample in processor 26 of the switching unit 20, is planned in such amanner, therefore, that the real-time-critical data telegrams consideredarrive in the processor 26 of the switching unit 20 at the latest at theswitching time or earlier. This eliminates the problem of timinguncertainties which become noticeable, in particular, in the case oflong transmission chains. Data which are intended, for example, for user18 and have been temporarily stored in the local memory 24 of theswitching unit 20 are retrieved from the latter at a given time,real-time-critical data are retrieved at the preestablished times andnon-real-time-critical data are retrieved during the section intendedfor them.

In consequence, as stated above, a simultaneous operation ofreal-time-critical and non-real-time-critical communication in the sameswitched data network and an arbitrary connection of additional users tothe switched data network are possible without disturbing the real-timecommunication itself.

FIG. 4 shows a diagrammatic representation of the interfaces between alocal user and a switching unit. According to the disclosed invention,the switching unit 40 is integrated in the user 39, for example acontrol computer 1 of an automation system. The user 39 participatesboth in the real-time-critical communication and in thenon-real-time-critical communication which is why real-time-criticalapplications 48, for example for controlling drives of an automationsystem, and non-real-time-critical applications 49, for example browsersfor spontaneous Internet communication or word processing programs, areinstalled in the user 39. For reasons of clarity, only logicalconnections and no physical connections, especially data connections,are shown. Communication between user 39 and integrated switching unit40 takes place via the local memory 41 in which the corresponding datatransmitted by the user 39 or intended for the user 39 are temporarilystored. Both the user 39 and the switching unit 40 must be able toaccess the local memory 41, the physical location of the local memory 41which is, for example, part of the switching unit 40 in the exemplaryembodiment shown, is of no significance in this connection. To guaranteethe separation between real-time-critical communication andnon-real-time-critical communication, and thus interference-freereal-time communication, two separate accesses to user 39 are required,one access being intended for the exchange of real-time-critical dataand the other access being intended for the exchange ofnon-real-time-critical data. As a consequence, the physicalcommunication takes place via two separate logical interfaces 42 and 43between the data network, not shown for reasons of clarity, and theswitching unit 40, and the logically separated communication channels 46and 47 between the memory 41, i.e. the switching unit 40, and the user39. The interface 42 and the communication channel 46 characterize thecommunication channels for the real-time-critical communication and theinterface 43 and the communication channel 47 characterize thecommunication channels for the non-real-time-critical communication.Considered physically, however, the two logically separated interfaces42 and 43 shown in each case and the communication channels 46 and 47are in each case the same communication channel which is used forconveying the respective data in both directions. In particular, theseparate signaling of which type of data are present and can beretrieved takes place via the two logically separated communicationchannels 46 and 47, the provision of real-time-critical data for thereal-time-critical applications 48 being signaled via communicationchannel 46 and the provision of non-real-time-critical data for thenon-real-time-critical applications 49 being signaled via communicationchannel 47. Thus, driver 44 and the real-time-critical applications 48can be processed with a higher priority than driver 45 and thenon-real-time-critical applications 49. Thus, the real-time-capableprocessing of real-time-critical data can also be guaranteed in user 39.In addition, separating the real-time-critical communication and thenon-real-time-critical communication, which is necessary forguaranteeing the real-time communication, has the advantage thatexisting programs, especially existing drivers, can be used withoutrestriction for the non-real-time-critical communication as a result ofwhich, on the one hand, no expensive new developments are necessary and,on the other hand, the further evolution of the non-real-time-criticalstandard communication has no influence on the real-time communicationitself and can therefore be included in the disclosed invention withoutany restriction.

In summary, the invention relates to a system and a method which, due toa cyclic operation, provides both for a real-time-critical communicationand a non-real-time-critical communication in a switched data networkconsisting of users and switching units, for example of a distributedautomation system. In a so-called transmission cycle (12), there is ineach case at least one section (13) for transmitting real-time-criticaldata and at least one section (14) for transmittingnon-real-time-critical data for all users and switching units of theswitched data network, as a result of which the real-time-criticalcommunication is separated from the non-real-time-criticalcommunication. Since all users and switching units are alwayssynchronized to a common time base, the respective sections fortransmitting data in each case occur at the same time for all users andswitching units, i.e. the real-time-critical communication takes placeindependently in time from the non-real-time-critical communication andis, therefore, not influenced by the latter. The real-time-criticalcommunication is planned in advance. Feeding-in of the data telegrams atthe original transmitter and forwarding them by means of the switchingunits involved takes place in a timing-based manner. Temporary storagein the respective switching units has the result that spontaneousInternet-capable non-real-time-critical communication occurring at anarbitrary time is shifted into the transmission section (14) of atransmission cycle (12) which is intended for the non-real-time-criticalcommunication and is also only transmitted there.

While the exemplary embodiments illustrated in the FIGS. and describedabove are presently preferred, it should be understood that theseembodiments are offered by way of example only. Accordingly, the presentinvention is not limited to a particular embodiment, but extends tovarious modifications that nevertheless fall within the scope of theappended claims.

1. A method of communicating in a distributed, industrial automationsystem, comprising: providing a plurality of user devices and aplurality of Ethernet switching units, wherein an Ethernet switchingunit is integrated in each user device; operating the plurality ofEthernet switching units via a common synchronous time base, wherein acommunication between the plurality of user devices and Ethernetswitching units is effected in transmission cycles, wherein eachtransmission cycle is subdivided into a first section for transmittingreal-time-critical data and a second section for transmittingnon-real-time-critical data, and wherein, for each transmission cycle, alength of the second section for transmitting non-real-time-criticaldata is automatically established by a length of the first section fortransmitting real-time-critical data; receiving at an Ethernet switchingunit real-time-critical data for a user device of the distributed,industrial automation system; transmitting the real-time-critical datato the user device during the first section of the transmission cycleintended for transmission of real-time-critical data; receiving at theEthernet switching unit non-real-time-critical data during thetransmission of the real-time-critical data; storing the non-real-timecritical data in a memory of the user device or the Ethernet switchingunit; transmitting the non-real-time critical data to a receiver duringthe second section of the transmission cycle intended for transmissionof non-real-time critical data.
 2. The method of claim 1, wherein aperiod of the transmission cycle is established at least once beforetransmitting the real-time-critical data.
 3. The method of claim 1,further comprising transmitting data for the organization of the datatransmission at a beginning of the first section.
 4. The method of claim3, wherein all Ethernet switching units in a network scheduletransmissions according to the transmission cycle having first andsecond sections.